Problem: $\dfrac{7}{5} - \dfrac{9}{8} = {?}$
$ = {\dfrac{7 \times 8}{5 \times 8}} - {\dfrac{9 \times 5}{8 \times 5}} $ $ = {\dfrac{56}{40}} - {\dfrac{45}{40}} $ $ = \dfrac{{56} - {45}}{40} $ $ = \dfrac{11}{40}$